Glass Failure Analysis of Tramp Glass

As a part of a product liability case, a glass failure expert was asked to determine if a piece of "tramp glass" found by a consumer (Upper left photo) was put into the bottle after it was opened. There was a companion bottle from the same six pack that also had glass contamination(upper right photo). If the tramp glass in the subject bottle was planted, then the glass in the "sister bottle" was also put in by the consumer. These were "twist off" bottles; therefore, it was decided that if the torque needed to remove the cap on the sister bottle was low, this would indicate the cap had been previously removed by the consumer. The removal torque was measured on the sister bottle, and it was twice that measured on control bottles. Thus, the cap on the sister bottle had not been removed, and the glass contamination entered this bottle during bottle manufacturing or bottle filling. From this it was concluded that the tramp glass in the subject bottle is also a manufacturing defect.